Protective helmet

ABSTRACT

A helmet is formed with a rigid outer shell and three energy-absorbing layers made of two types of CONFOR™ ergonomic, open-celled polyurethane foams. The first layer adjacent the rigid outer shell is a CONFOR™ CF-40 yellow foam and the middle layer is a CF-47 green foam, which is of greater stiffness than the outer layer. The inner-most layer is also a CF-40 yellow foam and, therefore, identical to the outer energy-absorbing layer. The three layers are 0.5″ thick. The helmet body is secured to a user&#39;s head with straps, affording a helmet design capable of continuously absorbing energy from multiple impacts while retaining the property of returning completely to its original shape. The multiple layering of materials having different stiffnesses results in the reflection of propagating stress waves through the materials, ultimately absorbing larger amounts of energy than the same materials not layered with alternating stiffnesses could absorb.

[0001] This application is a continuation application of U.S. patent application Ser. No. 09/127,125 filed Jul. 30, 1998.

[0002] The present invention relates generally to helmet construction and, more particularly, to a new and improved protective helmet for use primarily by persons engaged in sporting or other activities exposed to the risk of head injury.

[0003] Helmets used by bicyclists and others engaged in sports typically have a hard outer shell that covers energy-absorbing material. Bicycle helmets typically have a hard plastic outer shell that covers expanded polystyrene. Polystyrene absorbs energy by developing multiple micro-fractures throughout its structure. Once a polystyrene helmet develops micro-fractures it ceases to provide impact protection (i.e., such helmets are unusable after a single impact). Football helmets typically have a dense polyethylene outer shell that covers polypropylene pads capable of absorbing multiple impacts. Other helmets, such as those used by soldiers, typically have a metal or composite shell; that is able to protect a soldier's head from certain types of high-energy impacts.

[0004] Helmets typically have a retention system to secure the helmet in proper position on the user's head. The straps commonly used for bicycle helmets are difficult to adjust, resulting in many bicyclists wearing helmets improperly positioned and providing limited protection.

[0005] The helmet shape and the extent to which it covers the head are important design considerations. Helmets are shaped differently depending on the use to which the helmet is to be put and the energy level of the impacts the user might experience. Bicycle helmets are typically designed to protect the top, sides and front of the user's head.

[0006] A protective helmet or other impact/shock attenuation device or system must somehow absorb the kinetic energy of the impacting object or body before a large force reaches the place or body to be protected. This can be accomplished by maximizing the work done by the intervening material or system; that is, the product of the resisting force and the distance or deformation. If the resisting force is small and the distance or deformation is large, energy dissipated will be small; conversely if the resisting force is very large and the distance or deformation is small, their product, the work done by the system or material, and energy absorbed, will again be small. Only an appreciable resisting force, acting over some appreciable distance or deformation will ensure large energy absorption by the system or material.

[0007] Performance standards have been developed for certain types of helmets. For bicycle helmets, for example, the Snell B-95 Bicycle Helmet Standard involves a series of performance tests. A helmet passes the impact portion of the Snell test if it prevents a head from decelerating at a rate in excess of 300G's when subjected to a specific test impact. The Snell 300G's standard does not assure that a rider wearing a helmet meeting that standard will not suffer serious head injury. Head and brain injuries occur at deceleration levels well below 300G's; also, riders can experience impacts that result in head deceleration levels above 300G's.

[0008] The head can be thought of as having three components: the skull; the brain, which consists of compressible matter; and the fluid filling the skull and in which the brain floats. Neither the skull nor the fluid is compressible; the brain, however, is compressible and, when forced against the skull, does compress, bruising brain tissue and perhaps causing hemorrhaging. When the skull experiences an impact, the force is transmitted through the skull and fluid; the inertia of the fluid results in the brain moving in a direction opposite from that of the force applied to the skull. If that force is applied suddenly (i.e., there is an impact) and is substantial enough, the brain moves through the fluid and strikes the inside of the skull at a point roughly opposite to the area of the skull that sustains the impact.

[0009] When the brain strikes the skull with moderate force, the brain tissue in the area of the brain that hits the skull is compressed and bruised. That typically results in a temporary cessation of nervous function (i.e., a concussion).

[0010] When the skull is subjected to a more substantial impact, the brain typically hits the inside of the skull at a higher speed; a larger area of brain tissue is compressed and damaged and brain hemorrhaging is common (i.e. contusion results). If minimal hemorrhaging occurs, the individual may experience symptoms similar to those of a concussion. More substantial hemorrhaging may result in a loss of blood supply to the brain and even death.

[0011] When the energy level of the impact to the skull is substantial enough, the skull fractures. When it does, some of the impact energy is dissipated. A fracture may be either linear or localized. A linear fracture, the simpler of the two, is essentially a straight line crack. A localized fracture is one in which multiple fractures occur in a single area. In such a fracture, it is common for skull bone material to be displaced; the displacement can result in bone material penetrating brain tissue, causing hemorrhaging and swelling.

[0012] The present invention can be characterized in a variety of ways.

[0013] In one characterization, the invention provides an energy absorbing system having alternate layers of energy absorbing material layers.

[0014] In another characterization, the invention provides a helmet comprised of a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposition to each other. At least one of these impact-energy-absorbing material layers is made of an open-celled polyurethane foam.

[0015] The invention may also be characterized as a helmet comprising a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposed position to each other. The impact-energy-absorbing material layers, in combination with the relatively stiff outer shell, are selected so that the helmet will prevent a head from decelerating at a rate in excess of 100G's under the testing criteria employed.

[0016] The invention can also be characterized as a helmet comprising a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposed position to each other. In accordance with this characterization of the invention, the material layers are selected such that they are capable of restoring to their original shape following impact and/or repeated impacts.

[0017] In one embodiment, the present invention is directed to a helmet comprised of an outer shell, energy-absorbing layers, and a retention system for securing the helmet to the user's head. The energy-absorbing layers comprise at least a first layer of impact-energy-absorbing material adjacent to the outer shell, a second layer of impact-energy-absorbing material adjacent to the first layer, and a third layer of impact-energy-absorbing material adjacent to the second layer and to the wearer's head, wherein the second layer has a dynamic impedance higher than the first and third layers.

[0018] Although one embodiment is comprised of three layers of open-celled foam, it is theorized that the three layers may be replaced with four, five or more layers preferably each having lesser thickness than each layer in the three-layer embodiment to avoid construction of an unnecessarily large helmet. If four or more layers are utilized, the composite thickness preferably is the same as the thickness achieved in the threelayer design.

[0019] In another embodiment, the outer shell is preferably made of PETG (glycolmodified polyethylene terephthalate), which is a copolyester plastic having excellent impact strength, durability and the ability to be thermo-formed. Preferably, but not necessarily, the outer shell has an optimal thickness of 0.02 inch.

[0020] Also in one embodiment, the first of the energy-absorbing layers (i.e., the layer adjacent to the outer shell) is made of ergonomic, open-celled polyurethane foam, such as CONFOR™ foam manufactured by E-A-R Specialty Composites Corporation.

[0021] In another embodiment, the first layer is made of CF-40 yellow foam. The second layer is made of ergonomic, open-celled polyurethane foam having a higher dynamic impedance than the first layer. The second layer in this embodiment is made of CF-47 green foam. The third of the energy absorbing layers, the layer closest to the head, is made of the same material as the first layer. In this embodiment, therefore, the third layer is made of CF-40 yellow foam. Each of the three energy-absorbing layers is about 0.5 inch thick.

[0022] The foregoing materials were selected as a result of extensive testing of, and experimentation on, these and other foams.

[0023] The foregoing materials were also selected because of other important characteristics they possess, such as having low-impact, high-rebound properties. These materials conform easily to different shapes, such as the shape of a wearer's head, and are non-irritating in dermal contact.

[0024] An important feature of the invention is the multiple layering of energy-absorbing foams of different dynamic impedances (some or all of the layers may or may not have the same density). Dynamic impedance, z, is defined as the product of c, the speed at which a stress wave is propagated inside a material, and Y, the mass density of the material. The value of c is calculated as the square root of the ratio of the modulus, E, of the material and Y. The modulus, E, is experimentally determined to be the slope of a curve with dynamic stress on the vertical axis and dynamic strain on the horizontal axis. Dynamic impedance can be derived from either E or E*.

[0025] Viscoelastic materials, including polymer foams, are described in terms of viscoelastic (or elastoviscous) parameters to account for their reactions/deformations under both steady and vibrational forces. That is, these materials react partly as elastic (instantaneous, and recoverable deformation) materials, and partly as viscous (delayed and unrecoverable deformation) materials. Examples of viscoelastic parameters are the complex moduli (stress over strain) in extension, E*=E′+iE″, or in shear G*=G′+iG″, where E′, G′ measure the elastic resistance to extensional/compressional and shear forces, respectively; E″, G″ the viscous resistance to such forces. Alternatively, the response or deformation from extensional and shear forces is measured by complex compliances (strain over stress), D*=D′-iD″, J*=J′-iJ″, energy loss and attenuation in viscoelastic materials occur in proportion to the ratios (loss factors), E″/E′=G″/G′-D″/D′=J″/J′; in the same way the rate of deformation and recovery depends on the loss factor as described above. Materials with low values of the viscous modulus or compliance components compared to the elastic components will deform and recover rapidly, while those with high loss factors will react slowly, and absorb more energy when deformed under a given resistant force. The total resistance or stiffness (elastic and viscous) depends on the values E, G obtained from the square roots of the sum of the squared modulus components.

[0026] There is no relation, as such, between the stiffness of a viscoelastic foam or other viscoelastic material, the rate of deformation under loading forces, and the rate of recovery when the loading stops. That is, viscoelastic materials, including polymer foams, react to forces partly as elastic, instantaneous responding materials, and partly as viscous, delayed responding materials. Viscoelastic material stiffness is determined by two components of a modulus (stress/strain), E*=E′+iE″ (extension), or G*=G′+iG″ (shear), where E′, G′ are the elastic modulus components, and E″, G″ are the viscous modulus components. The rate of deformation under loads, and the rate of recovery when loads are removed depend on the ratios E″/E′-G″/G′, not the magnitude of the total stiffness moduli, E=[(E′)2+(E″)2]½ or G=[(G′)2−(G″)2]½. Thus a foam may be: a) soft and have slow recovery, or stiff and have slow recovery, b) soft and have fast recovery, or stiff and have fast recovery.

[0027] The layering pattern of such foams having differing dynamic impedances can result in a structure that reflects propagating stress waves upon impact through the materials and that ultimately enables the structure to absorb larger amounts of energy than the same individual material not layered with alternating dynamic impedances. The foregoing layering pattern of the invention was selected following extensive experimentation and calculation.

[0028] The multi-layer foam design of the present invention reduces the amplitude of a stress wave before it reaches the head. This reduction of the amplitude of this impact-induced stress wave is equivalent to reducing the amplitude of the deceleration force experienced by the head.

[0029] The three-layer foam embodiment of the invention was developed with the objective of dissipating a substantial percentage of the initial impact-induced stress wave energy by causing a sequence of internal reflections of the stress wave. The three layers, in order moving from the outside inward, were selected to have (1) a low dynamic impedance, (2) a higher dynamic impedance, and (3) the same dynamic impedance as layer (1). This sequence is shown to optimize the internal reflections of the stress waves. By causing these numerous internal reflections, the conversion of deformation energy into heat is maximized—therefore minimizing the amount of the stress wave that is allowed to propagate into contact with the wearer's head.

[0030] The retention system preferably comprises three separate straps. The first strap is wrapped around the front of the head and attached to an occipital support. This first strap is elastic and is independent of the rest of the strapping.

[0031] The second strap is preferably looped through two holes formed in the shell and the foam layers and is pulled down over the ear in a V-shaped form. The third strap is symmetric to this strap on the other side of the helmet. Preferably, two individual straps are used, rather than a single strap. (A single strap is used in many helmets today.) Other retention systems can also be used.

[0032] An advantage of using open-celled polyurethane foam, such as the CONFOR™ foam, is that it can withstand multiple impacts. The helmet of the present invention absorbs energy notwithstanding multiple impacts; it also rebounds, beneficially returning to its original shape over time. Therefore, the helmet of the present invention can be used over and over again; it does not have to be replaced after a single impact. Indeed, if in a single accident the helmet receives more than one impact, the foam's properties, including its ability to retain shape, advantageously insure that the helmet maintains its integrity and purpose. In contrast, most helmets currently in use dissipate energy by cracking. Once such a helmet has dissipated energy it will not protect against injury and must be discarded.

[0033] The aforementioned novel use of the CONFOR™ material is complimented by the further advantage that the material is soft and extremely comfortable, in contrast to the rigid expanded polystyrene commonly used today.

[0034] Although the preferred embodiment features three layers of impact-energy absorbing, open-celled polyurethane foam, the scope of the invention contemplates additional energy-impact-absorbing layers as may occur to persons skilled in this art following review of the novel disclosure herein. In some circumstances, it is theorized that the objects of the invention may be achieved with two layers of open-celled polyurethane foam (e.g., CONFOR™ materials), appropriately sized and dimensioned in thickness.

[0035] It is within the scope of this invention to utilize energy-absorbing layers of varying thickness and not necessarily the same thickness as in the preferred embodiment.

[0036] One or more comfort pad strips may be attached to this exposed inner surface to allow air to circulate between the helmet and head without denigrating the performance characteristics of the helmet.

[0037] Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

[0038] For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:

[0039]FIG. 1 is a side elevational view, having a partial cross section, of the helmet structure of the present invention with retention straps omitted for clarity;

[0040]FIG. 2 is a side elevational view of the helmet of FIG. 1 with only one V-shaped side strap shown for clarity;

[0041]FIG. 3 is a front elevational view depicting an occipital support; and

[0042]FIG. 4 consists of a schematic top view and a left side view of a human head depicting frequency of impact on different regions of a bicyclist's head based on empirical data.

DETAILED DESCRIPTION OF THE INVENTION

[0043] Refer now to FIG. 1 where a helmet, generally indicated by reference numeral 10, that is constructed in accordance with the principles of the present invention is depicted. For convenience, helmet 10 is depicted in an upright position as helmet 10 would normally be worn by a wearer, although the orientation depicted is for clarity of description only and the helmet is not limited to the orientation depicted.

[0044] The present invention is believed to be applicable to a wide range of activities, including but not limited to, bicycling; motorcycling; auto racing; skiing; snow boarding; horseback riding; ice skating; roller skating; inline skating; hang gliding; climbing; spelunking; laying football, hockey and other sports; and working, such as performing construction work. Other applications, besides helmets, may include elbow/knee pads, cushions (car or seat), and bumpers.

[0045] Helmet 10 has a dome shape and is approximately 4 ½″ high by 8 ½″ long. Helmet 10 includes an outer shell made of copolyester plastic (e.g., PETG) having a thickness of between 0.02″-0.125″ with 0.02″-0.03″ being a preferred thickness range. PETG film is available from Eastman Kodak and is called “Kodar PETG copolyester 6763”.

[0046] Adjacent to the inner surface of outer shell 12 is a first layer of CONFOR™ CF40 yellow foam (layer 14). Adjacent to the inner surface of layer 14 is a second layer of CONFOR™ CF-47 green foam (layer 16). CONFOR™ CF-47 green foam has a higher dynamic impedance than CF-40 yellow foam. Adjacent to the inner surface of layer 16 is a third layer of CONFOR™ CF-40 yellow foam (layer 18). Layers 14, 16 and 18 are each approximately ½″ thick. Layers 14, 16, 18 are placed one upon another and layers 14,16, and 18 conform their shapes to that of the outer shell 12 creating a cavity for receiving a portion of the user's head.

[0047] CONFOR™ foams are open-celled polyurethane foams from E-A-R Specialty Composite Corporation. These foams are multiple-impact foams, are excellent for energy absorption, are effective under compression, and are soft and flexible. They are also breathable and non-irritating in dermal contact. They conform to any shape, come in varying stiffnesses and dynamic impedances, cushion well against shock and vibration, and have a slow rate of recovery after deflection, thus eliminating the secondary impact effects that would occur if the rate at which the material recovered its pre-impact shape were too rapid.

[0048] Several comfort pad strips can be positioned on the surface of layer 18 adjacent to the wearer's head to provide a gap between layer 18 and a wearer's head to allow air to flow therebetween. Each of the layers of foam 14, 16 and 18 can be bonded together with an adhesive. Such adhesive has a minimal effect on the ability of the foam to absorb energy.

[0049] A plurality of vents, 32, 34, are formed in helmet 10. Layers 14, 16 and 18 are continuous sheets of material except for the vents 32, 34.

[0050] Refer now to FIG.s 2 and 3 where a retention system is depicted. A first strap 50 is looped through a pair of vertical slots 52, 54 and a portion of the strap extends in a longitudinal direction on helmet 10. Vertical slots 52, 54 each extend through helmet 10 from an outer surface of the outer shell 12 through an inner surface of layer 18. The two ends of strap 50 are looped through the vertical slots and are pulled down over the ear in a V-shaped form through a retainer 56 and through a buckle 58. The second strap on the other side of the helmet is symmetric to the first strap; a male fastener (not shown) would be used to mate with fastener 58. In most conventional helmets, a single strap is used to form the V-shape on both sides. The use of two separate straps makes easier adjustment. The retention straps are available from American Cord and Webbing Co., Inc. of Woonsocket, R. I. The length of strap 50 can be adjusted to suit the needs of the wearer. The side straps use nylon webbing that is 1″ wide.

[0051] In FIG. 3, an occipital support 70 is depicted. Occipital support 70 is secured to helmet 10 by an elastic strap 72 that is independent of the other two straps.

[0052] Many potential impact-energy-absorbing materials, both single- and multiple-impact, were tested; various thicknesses of the materials were tested; several possible outer shell covers were also tested. These materials were then layered in a number of different combinations and tested to gain a greater understanding of the propagation and reflection of stress waves in these materials.

[0053] Helmets made according to the present invention achieved head deceleration levels of 85.7G's and 90G's; in certain tests, helmets constructed according to the present invention achieved decelerations as low as 76G's. In contrast, a football helmet we tested provided results of approximately 156G's, and a single-impact bicycle helmet we tested provided results of approximately 285 G's.

[0054] It will be readily seen by one of ordinary skill in the art that the present invention fulfills all the objectives set forth above. After reading the foregoing specification, one of ordinary skill will be able to effect various changes, substitution of equivalents and various other aspects of the invention as broadly disclosed herein. It is, therefore, intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof. 

1. A helmet, comprising: a) a stiff shell having an inner surface; and b) a plurality of impact-energy-absorbing material layers disposed within said shell in superposed position to each other, the layers having differing dynamic impedances; all of said layers being continuous; and one of said layers being adjacent to and coextensive with substantially the majority of said inner surface of said shell; said shell having a stiffness greater than said layers.
 2. The helmet of claim 1, further comprising straps operatively connected to at least one of the shell and plural layers to secure the helmet to a user's head.
 3. The helmet of claim 1, wherein at least one of the impact-energy-absorbing material layers are made of polymeric material.
 4. The helmet of claim 1, further comprising vents formed in said helmet.
 5. The helmet of claim 1, wherein the dynamic impedances of the layers are in a pattern of low, high, low with respect to each other.
 6. A protective device, comprising a stiff outer shell having an inner surface, and inner layers of energy-absorbing material, said layers superposed on each other; one of said layers being in direct contact with the shell; the layers having differing dynamic impedances; said shell having a stiffness greater than said inner layers.
 7. The protective device of claim 6 wherein the energy-absorbing material layers are co-extensive with substantially the majority of the inner surface of the shell.
 8. The protective device of claim 6, wherein the device contains at least three inner layers of energy-absorbing material.
 9. The protective device of claim 6, wherein the energy-absorbing material is a foamed polymeric material.
 10. The protective device of claim 6 wherein the layers of energy-absorbing material are positioned with respect to one another so a layer of low dynamic impedance is adjacent to a layer of high dynamic impedance.
 11. An energy-absorbing system comprising alternating layers of energy-absorbing material having different dynamic impedances.
 12. The energy-absorbing system of claim 11, wherein the device contains at least three layers of energy-absorbing material.
 13. The energy-absorbing system of claim 11, wherein the energy-absorbing material is a foamed polymeric material.
 14. The energy-absorbing system of claim 11, wherein the layers of energy-absorbing material are positioned with respect to one another so a layer of low dynamic impedance is adjacent to a layer of high dynamic impedance.
 15. The energy-absorbing system of claim 11 wherein outer surfaces of the energy-absorbing system comprises an energy-absorbing material layer having a lower dynamic impedance than the layers adjacent to the outer surfaces.
 16. The energy absorbing system of claim 11, wherein the system reduces the amplitude of any applied stress wave to the outer surface of the system.
 17. The energy-absorbing system of claim 11, wherein the system allows for numerous internal reflections of any applied stress wave to the outer surface of the system. 